Teaching machine in which instruction items are projected by an image projector

ABSTRACT

A strip film, carrying instruction items and questions with response indications thereon, and additionally, coded response code tracks (which are blocked from view of the student) is projected on a screen; the student is provided with a pointer having a photosensitive end, responding to the response items. A movable mask scans across both the response items and the response code track, and electrooptical transducers transmit the pulses upon scanning of a code position on this code track and the pulse from the photosensitive end to a logic circuit, which determines which code track has time-coincidence with the pulse from the photosensitive end. Subsequent indexing of the film to further instruction items (which may be entirely new instruction items or sub-items in further explanation in case the answer was wrong) is then controlled by the logic circuit decoding the coincidence of indication from a particular track and the photosensitive end.

United States Patent Laplume [541 TEACHING MACHINE IN WHICH INSTRUCTIONITEMS ARE PROJECTED BY AN IMAGE PROJECTOR [72] Inventor: JacquesLaplume, Gif-Sur-Yvette, France Societe DEtudes Techniques etDEntreprlses Generales (SODETEG), Le Plessis-Robinson, France 22 Filed:Sept. 4, 1970 [21] Appl.No.: 69,739

[73] Assignee:

6/1968 Kilby..... ...35/9A 3/1970 Gaven ..35/9A Primary ExaminerWm. H.Grieb Attorney--Flynn & Frishauf [57] ABSTRACT A strip film, carryinginstruction items and questions with response indications thereon, andadditionally, coded response code tracks (which are blocked from view ofthe student) is projected on a screen; the student is provided with apointer having a photosensitive end, responding to the response items. Amovable mask scans across both the response items and the response codetrack, and electrooptical transducers transmit the pulses upon scanningof a code position on this code track and the pulse from the photosensitive end to a logic circuit, which determines which code track hastime-coincidence with the pulse from the photosensitive end. Subsequentindexing of the film to further instruction items (which may be entirelynew instruction items or subitems in further explanation in case theanswer was wrong) is then controlled by the logic circuit decoding thecoincidence of indication from a particular track and the photosensitiveend.

14 Claims, 7 Drawing Figures q n" "6a E -7a We R PATENTEDmwao I9723.665.615

sum 10F 4 Cl n N Lcsczqg:

,5a i "6a f Ti H TEACHING MACHINE IN WHICH INSTRUCTION ITEMS AREPROJECTED BY AN IMAGE PROJECTOR Cross reference to related applications:

The present invention relates to teaching machines and more particularlyto teaching machines in which instruction items are projected by meansof an image projector, such as a film strip projector and projecting,for instruction purposes,

instruction items such as text material, figures, and the like, coded ona film, on a screen for presentation to a student.

Teaching machines of the type to which the present invention relatesprovide programmed instruction items which are presented to one or morestudents. The instruction items may contain text material, drawings orfigures, and the like. Each instruction item should be complete initself and made a definite pedagogical point which invites the studentsto reflect and ponder, and then answer questions which are listed andreferred to hereinafter as response items. The questions should be sophrased that they permit a judgment to made regarding comprehension ofthe instruction item by the student. The response items are preferablyof the multiple choice type and so presented that they offer a studentan opportunity to select among various responses to one which is mostappropriate. The choice of the responses is indicated by the student bymeans of a device placed at his disposal; such a device may, forexample, by a keyboard, or, for example, a pointer which the studentpoints to a spot on the item which is presented to him and which thestudent believes is the correct one; or, another analogous and similardevice may be used to translate the student s response into machinelanguage" which can be accepted by automatic, electronic equipment. Themachine itself is programmed to detect whether the answer proposed bythe student is correct, or false. In case the answer is correct, thesubsequent instruction item is automatically presented to the student,together with a series of questions testing the comprehension of thenext instruction item. If, however, the answer supplied by the studentto any instruction item is incorrect, the machine presents a subsequentsub-instruction item to the student which provides more detailexplanations regarding the material presented by the preceding maininstruction item, in order to guide or lead the student to answercorrectly to the questions posed thereafter. These sub-instruction itemsneed be of variable number and need be placed in different mannersbetween the items, in accordance with the type of teaching machine underconsideration. In a general way, and when located on paper tapes, theyare frequently placed between successive main instruction items.

Paper tapes, and other sequential tapes usually carry on a portion ofthe tape prevented from access by the student the correct answer to thequestion, this answer being in the form of a code, and an auxiliarydevice placed at the students disposal to deliver an answer in a similarcode. The written response, that is the read-in response into theteaching machine and the response previously recorded on the tape orband are then compared in certain logic circuits to determinecoincidence, indicative of a correct answer, or non-coincidenceindicative of a wrong answer.

Teaching machines of this type may have various differences among eachother and specifically by the means placed at the disposal of thestudent in order to convert his answer into machine readable language sothat the reply intended by the student can be electronically recorded.

In teaching machines in which the student is provided with a keyboard,similar to that of a typewriter keyboard, for example, each key may beassigned a certain symbol or a number in particular order. This system,if a full complete alphanumeric typewriter-type keyboard is used may bequite complicated.

Smaller keyboards may require special construction. It has thus alreadybeen proposed to utilize a pointed element which is placed in selectedholes in order to indicate a specific answer, placement of a pointer ina specific socket completing the continuity of an electric circuit, sothat information is obtained which can afterwards be processed todetermine if the answer is correct or wrong, and thereby control thesubsequent functioning and operation of the machine. Other pointerssimilar to photostylii have been suggested, require, however,presentation of the instruction item on a televisiontype screen which isa complicated and quite costly solution, particularly with a largenumber of teaching positions to be filled.

It is therefore an object of the present invention to provide a meansfor the student to indicate the particularly selected response which issimple, can be used by various students, and can be inexpensivelyinstrumented.

Subject matter of the present invention In accordance with the presentinvention, images corresponding to items and sub-items of instructionalitems are located one after the other in sequential frames on a film,the sub-items being located between successive main instruction items.The different images carrying the instruction items are projected on ascreen, successively, in accordance with indexing of the film. Eachimage presents, in the portion visible to the student, besides theinstruction items questions, free, clear spots which correspond, on theportion film hidden from view of the student, to equal clear spotsplaced on parallel tracks extending in the direction of indexing of thefilm.

The student is invited to selected the one or the other of the responseitems by placing a pointer with a photosensitive end piece on the screenat the point of the bright spot indicative of a selected response item,which action triggers operation of a mask successively and brieflyblocking the bright spots of the response items on the film, as well asthe spots on the code track, to obtain output pulses from thephotosensitive end of the pointer, as well as from optical-electrictransducers located in light-receiving relationship with respect to theresponse code tracks. Of course, rather than blocking a light path, apreviously blocked opaque area may be illuminated and pulses indicativeof brief light reception, rather than brief darkening may be utilized.

The photoelectric transducers located in light-receiving relation withrespect to the coded tracks deliver pulses when the specific spotcorresponding to a response item is darkened by the mask. Logic circuitsthen decode the information obtained from the coincidence of pulses fromthe photoelectric transducers and those obtained from the photosensitiveend of the pointer, placed by the student on a selected response item toobtain a coicidence which will be characteristic of the moment, in time,when the luminous flux changes, due to the darkening of the spot on theresponse item. If the response item corresponding to the correct answerhas been indicated, then the maximum number of instruction items on thefilm will be indexed; if a different response has, however, beenrecorded, then an instruction item giving further explanation tocorrect, and further amplify the understanding of the student can bepresented.

The invention will be described by way of example with reference to theaccompanying drawings, wherein:

FIG. I is a fragmentary plan view of the film;

FIG. 2 is a schematic side view of the projection system;

FIG. 3 is a schematic plan view of the film and the projection systemand illustrating the film reading;

FIG. 4 is a detailed view of the optical reader of FIG. 3;

FIG. 5 is a schematic cross sectional view of the pointer with aphotosensitive end, to be used by the student;

FIG. 6 is a schematic circuit diagram of a logic circuit to process theinformation obtained from the photoelectric transducers of FIG. 4, andthe pointer of FIG. 5; and

FIG. 7 is a schematic circuit diagram of a different embodiment of thelogic circuit.

The film 1 has lateral perforations 2 to locate the film, properlyframed, in a projector, as is well known. One of the edges of the filmis formed with longitudinal tracks a,b,c,d,... for example four, asillustrated in FIG. 1. The number of these tracks should correspond tothe largest number of sub-instruction items intended to be used in theparticular instruction program.

Each one of the complete instruction items carries a text 4 which may,for example, be additionally illustrated by drawings, figures and thelike. Each one of the text items 4 is followed by one or more questions.The answers to the questions for example in the form of multiple choiceare represented by blank spots 5, 6, 7, 8. These spots need notnecessarily be located one underneath the other; the only requirement isthat they are off set, or spaced, with respect to each other in thesense of indexing or movement of the film, or, in other words, presentsequentially, with respect to an end of the film different longitudinaldimensions. Each one of the spots 5-8, and at the same horizontalalignment, has a corresponding bright or clear spot 5a, 6a, 7a, and 8a,each one located on one of the tracks a-d. The tracks a-d, and thereforethe spots 5a-8a are blanked from view of the student. FIGS. 2 and 3illustrate, in schematic form, the image projection system. A strip film3 rolled on spools 9, l0 and guided by idlers 11 is moved by motor 13driving a sprocket 14. Movement of the motor is likewise applied to thespools 9, by means of a drive 15, which always maintains the film inproper tension. The optical system of the projector is formed by a lamp16, a condenser 17, a projection lens 18 and a screen 19. To theseelements, all well known by themselves, is added an optical-electricaltransducer assembly formed of photoelectric devices generally indicatedat 20, and a mask, or blocking element 12. The optical-electricaltransducer assembly, seen in more detail in FIG. 4, is formed of as manyphotoelectric transducer cells 21, 22, 23, 24 as there are tracks a, b,c, d, that is, in the selected example there will be four photosensitivecells. Each one of the photosensitive cells receives light from thebright spots 5a-8a located on a corresponding track. So that thephotoelectric cells may receive the light from a spot regardless of itsposition on the track, within a frame, light conduits 25-28 areprovided; these light conduits may be mirror assemblies, prisms, orlenses, or any other equivalent optical device. These devices can beinterposed between the photosensitive cells and the film if thephotosensitive surface does not cover the entire height of a frame, orthat portion which carries the bright spots 5a-8a. Light guides, orsimilar elements may be used, for example particularly as shown at theright hand side of FIG. 4. Thus, if a frame is correctly centered, thephotosensitive cells 21-24 are permanently excited by the light whichtraverses the bright spots 5a-8a. The entire assembly of cells iscovered by a housing to afford mechanical protection and to preventprojection of the tracks on the screen 19, so that the position of thecoded response spots 5a-8a will be blocked from view of the student. Thestudent may thus only see the instruction item, and, as illuminatedbright spots on the screen, the spots 5-8 following the variousquestions.

As previously mentioned, the student indicates his response by means ofa pointer applied to one or the other of the luminous bright spots 5-8.The end of the pointer (FIG. 5) is provided with a photosensitive cell29 which, upon its application on the screen, depresses spring 30 tocause closing of contacts 32, 33 by means of push button 31. Closing ofcontact 33 connects the pointer, and particularly photosensitive end 29into electric circuits, or establishes its interconnection with theoutput. Other, manually controlled switches can be used. As soon as thepointer is excited by the light of a bright spot, it will supply anoutput voltage. The closure of the contact 33 places an electromagnet 50(FIGS. 2, 3) into circuit, which operates a plunger, causing rapidvertical displacement of a mask, or blocking element 12 extending acrossthe image, the blocking element 12 traveling along the length of thefilm. The blocking element or mask 12 may, for example, be simply anopaque rod, or it may be a transparent strip on which an opaque tracehas been placed. The mask should be just slightly greater than theheight of the spots 5, or 50. Upon movement of the mask, it willpartially interrupt the light emanating from lamp 16 and lens 17. Thespots 5-8, as well as the spots 5a-8a will thus briefly be masked. Atthe moment of blocking, the current applied by the photocells 21-24, aswell as the current applied from the photocell 29 at the photosensitiveend of the pointer (FIG. 5) will fall to zero or null, and then, afterpassage of the mask, will again take its initial value. This sudden dropprovides a pulse which, upon application to a logic circuit, causesindexing of the film and recording of the answer, and its type, that iswhether it is correct or wrong.

Let one, for example, suppose that the pointer is placed at the spot 8(FIG. 1). The pulse from photocell 29 will thus occur at the same timeas the extinction of the spot 80, which, as has been noted, is placed inthe first track a on film 1. Thus, the outputs from photocells 21, and29 will be simultaneous. If, on the other hand, the student has placedthe pointer at the spot 7, a coincidence of pulses will be obtained fromphotocell 24, assigned to track d, as well as photocell 29.

The information obtained from the simultaneous occurrence of a pulsefrom photocell 29, that is from the pointer, and the specific trackhaving a spot aligned with one on which the pointer has been placed isthen processed in a logic circuit, as illustrated schematically in FIG.6. The logic circuit of FIG. 6 determines if the answer is correct orwrong, and controls a sequence of operations in accordance with theresult obtained.

A correct answer will result in indexing of film by a maximum number offrames, since further explanatory sub-items need not be projected to thestudent; on the other hand, an indication that a wrong answer has beenfurnished, and, further, which one of the wrong answers causes indexingof the film in accordance with a different pattern. These furtherexplanatory sub-items are inserted between consecutive main instructionitems.

Pulses applied by photocells 21-24, shown schematically in FIG. 6, aswell as photocell 29 (shown at the left of FIG. 6) are transmitted to agroup of AND circuits 34-37 over differentiating circuits 210-213, aswell as 290, which permit the passage of pulses but which block d-ccomponents. Coincidence between pulses from pointer cell 29 and fromcell 21 enables AND circuit 34, which applies an output to a terminal 38of a preset counter 42 applying a pulse to counter 42 at terminal 38 andcauses the counter to supply an output of 1; at 39, an output of two, at40, an output of three, and at terminal 41, an output of four. At thesame time, an output from any one of the AND gates 34-37 is applied toOR gate 43, which causes bistable circuit 51, for example, an ordinaryflipflop, to trigger and to switch state, exciting a relay 52 andstarting motor 13.

Each time that film 1 has passed a frame, a mechanical device connectedto the sprocket 14, and not shown in FIG. 2, provides a pulse which isapplied to an input 44 of counter 42, to reset the counter by one count.When the counter has reached zero, output from terminal 45 resetsflipflop 51 to change it to the ZERO state, thus dropping out relay 52and stopping motor 13.

Coincidence between pulses from photocells 29 and 21 positions thecounter 42 to a count of one, and movement of the film will thus stopafter one frame. If, for example, the student has designated with hispointer not the response item 8, but rather the response item 7, thencoincidence between pulses the cell 29 in the pointer, and the cell 24would have been detected, enabling AND gate 37, causing indexing of thefilm by four frames. During movement of the film, an auxiliary contact47 of the relay controlling operation of the motor is opened to cut theconnection between the photosensitive cell 29 of the pointer and the ANDgates 34-37, in order to avoid recording of parasitic signals whichoccur during rapid passing of the spots 5-7 under the pointer if itcontinues to be applied to the screen.

The position of the bright spots 5a-8a along the length of the tracksa-d is predetermined for each image frame in such a manner that themachine will automatically present appropriate instruction item, be itthe main, or a subsidiary instruction item, as determined by the answerdesignated by the student. For example, in the embodiment described inconnection with the present invention, the correct answer corresponds tospot 7, producing the maximum indexing of frames, that is, presentationof the next main instruction item and no subsidiary instruction items.

If the student tries to designate an image point which has no horizontalalignment with one of the spots 5a-8a, or, which is saying the samething, between 5 and 8, then the logic circuit will not detect anycoincidence, circuit 43 will not supply any output signals and the motor13 will not start.

As soon as the motor starts under control of relay 52, the mask 12 isreturned to its initial position by spring 53. This can easily beobtained, for example, as shown in FIG. 6 by interrupting continuity ofthe circuit to electromagnet 50 by interconnecting contacts 69 betweenthe connection from contact 33 and solenoid 50, that is, by addinganother group of contacts to the contact bank controlled by relay 52.

The signals obtained from AND gates 34-37 are further utilized in orderto determine if the response selected by the student is correct, orwrong, it being understood that the correct answer will be desirablythat one which causes indexing of the maximum number of frames on thefilm, since the sub-instruction items are interposed between the maininstructional items.

If track d has at least one clear, bright spot, the photosensitive cell24 is excited and provides at its output 54 a voltage which opens ANDgate 55 simultaneously, and gates 56, 57 are blocked since voltage fromcell 24 is applied to inverse inputs of AND gates 56, 57. If the track dis completely opaque, but track c carries at least one bright spot, thenno voltage will appear on line 54, and AND gate 55 will be blocked, butAND gate 56 will provide an output to enable AND gate 58. Similarly, ifboth tracks c and d are opaque, but track b carries at least onetransparent spot, then only the circuit 59 will be enabled. Condensersin parallel to the inputs of the AND gates 55, 58, 59 act as chargestorage devices to prevent modification of the state of the gates duringthe brief moment of blocking of the bright spots by the mask. In thecase of example of FIG. 1, the correct answer will always be representedby a bright spot on the track d. If the student correctly identifiesspot 7 (FIG. 1) on the response item, AND gate 55 will be the only onewhich is enabled. By correctly responding, a pulse will also be obtainedfrom AND gate 37 upon scanning by the mask. The AND gate 37, togetherwith the enabling of line 54 will enable circuit 55, a pulse will betransmitted to OR gate 60 to be applied to AND gate 61 and the inverseinput to AND gate 64. Since an output will be obtained from OR gate 43,AND gate 61 will be enabled providing an output to counter 62, whichcounts the correct answers, and further enabling an indicator 63indicating the correct answers.

If the student had answered incorrectly, for example by placing thephotosensitive end 29 against the luminous spot 5, the pulse fromcircuit 36 cannot enable AND gate 58, so that circuit 61 will remaindisabled. Circuit 64 will, however, be enabled since a pulse from ORgate 43 will be accepted, causing the wrong counter 65 to step by onecount and causing the wrong" indicator 66 to light.

If the instructional material can be so arranged that only a singlesub-item is interspersed between main instruction items, then thesignals can be processed in a simplified circuit; referring now to FIG.7, which illustrates a simplified variation of the logic circuit of FIG.6: if the answer supplied by the student is wrong then pulses from thephotosensitive end 29, and the single photocell 70 which is required toscan the response track will not occur simultaneously, and no pulse willbe obtained from the output of AND gate 71. Flipflop 72 will remain inits initial state of ZERO and will supply at its output 73 andunblocking voltage to the AND gate 74. Upon closing of contact 33, whichstarts scanning of the mask, the differentiating circuit 75 will have apulse applied thereto which is transmitted by a delay circuit 76. Thedelay introduced by circuit 76 is slightly greater than the duration ofthe scanning of the mask. The pulse from circuit 76 will be applied toAND gate 74 which, now, will open and cause the wrong" counter 77 toincrease by one count, simultaneously indicating the wrong answer onindicator 84. At the same time, the flipflop 78 will change to stateone, relay 52 will start and cause operation of the motor to index thefilm. As previously indicated, opening of contact 47 prevents spuriouspulses, and the application of spurious signals to AND gate 71. As soonas the film has indexed by one frame, a pulse is supplied over line 79by the film advance mechanism, which opens AND gate 80, enabledadditionally by the output from line 73 of flipflop 72, which, in turn,resets flipflop 78 to stop the motor by dropping out relay 52. Theprojector thus will present the single sub-instructional item givingadditional explanations to the student to lead him to the correctanswer.

If the student had initially responded with the correct answer, thepulses from photocells 29 and 70 would have arrived at circuit 71 incoincidence. Output from circuit 71 will have caused the correct"counter 81 to step by one count, simultaneously indicating the correctanswer on the indicator 83. Additionally, flipflop 72 would change tostate one, causing a potential on line 73 to disappear and block ANDgate 74. Thus, when a pulse is obtained over the delay line 76, the ANDgate 74 cannot be enabled and the wrong" counter remains unaffected. Aspreviously indicated, pulses from delay element 76 do, however, changethe state of flipflop 78. Relay 52 will thus pull in and cause motor 13to start. At the subsequent image, the pulse on line 79 by themechanical transport will, however, find AND gate blocked since there isno output on line 73 from flipflop 72. Thus, flipflop 78 will remain inthe state of ONE, and motor 13 will continue to run.

The output pulse from line 79, controlled by the indexing mechanism ofthe film advance is applied additionally to a delay element 82 and willhave just stopped when the flipflop 79 passes again to state ZERO, inorder to open AND gate 80. Passage of the film will continue until thesecond frame is presented. At that moment, a pulse from line 79 now willfind AND gate enabled over line 73, causing dropout of the relay 52 andstopping of the motor. Thus, upon supplying the correct answer, twoframes of the film run before the film again stops.

Various changes and modifications are possible, and only two specificexamples have been described. Specifically, the logic circuit and therelay may be replaced by other similar elements having similarfunctions. The tracks a, b, c, d and the photosensitive cells with whichthey are associated may be located at any desired place on the frame ofa picture. They may, for example, not be arranged in horizontalalignment but rather in longitudinal alignment between consecutiveimages, the scanning of the mask 12 then being done transversely, ratherthan longitudinally, with respect to movement of the film, the spots 5-8being themselves spaced transversely with respect to each other, ratherthan longitudinally. The response of the student will thus be, withrespect to a specific point on the abscissa, rather than with respect tothe ordinate, considering each frame itself as a set of points inorthogonal coordinates.

The mask itself may be formed of two movable masking elements, onemoving in a horizontal direction and the other transversely, withrespect to the longitudinal extent of the film, so that the responsecode tracks, and the position of the photosensitive end of the pointercan be combined in two directions, to enable identification of theresponse of the student by designation on the screen of a specificcoordinate point, and not only by a horizontal, or vertical locationwithin a frame.

The optical ribbon may be located adjacent the film on the tracks a, b,c, d; this is not necessary, and the photosensitive elements may beplaced adjacent the screen 19 and in light receiving relationship withthe images of the response code tracks. This solution is particularlydesirable for small size film, and enables use of much larger readingelements, since they will respond to an enlarged image. This advantageis, obtained only at the cost of diffusion of the light on the screenand possible decrease of difference between brightness and darkness, asthe mask passes over the frame during scanning. The mask, itself, canmove parallel any direction, or in the form of a rotating shutter havinga slotted blade moving in a plane parallel to the film plane. In thearrangement, the bright spots such as spots and 5a will then be alignednot along a transverse line, but rather along a similar radius withrespect to the center of rotation of the rotating shutter. The maskitself may be a rod, any kind of blocking element, or a blade, such as ashutter blade having a width equal to that of a projected light spot, orlarger.

The fixed photocells 2124 may be replaced by movable cells, connectedfor movement conjointly with the mask 12, and responding to the widthonly of the bright spots 5a-8a. Upon scanning by the mask, coincidencebetween the abrupt decrease in luminous flux obtained from thephotosensitive end 29 and the abrupt increase of light flux obtainedfrom the respective photosensitive element 21-24 is detected. Thus, theparticular track carrying a bright spot is identified with respect tothe specific answer indicated by the student.

The optical system has been described essentially in connection withbright light falling on photosensitive elements; the system may bereversed, and tracks may be transparent on which opaque spots areformed, coincidence between decrease of light sensed at any point by thepointer of the student and, on the other hand, by the photosensitivecell associated with the response code tracks can then be detected.

In accordance with another variation, sub-instructional items need notbe placed longitudinally, that is interspersed with main instructionalitems on the film, but can be placed rather at the side of correspondingmain item. The sub-items are then presented, for example, not byindexing of the film but rather by unblocking portions of a frame,previously masked to the student by means of a movable mask arranged toselectively permit presentation of sub-items, as desired. Of course, allsub-items could be projected simultaneously with directions to thestudent to first answer a group of questions which, if correctlyanswered, will cause indexing of the film to the next main item or, ifincorrectly answered, will remain exposed to the student for furtherconsideration and study until a next answer is given or until apredetermined time has elapsed. Various other changes and modifications,within the inventive concept, may be made as desired by the teachineprogram to be presented.

I claim:

1. Teaching machine comprising an image projector projecting sequentialimages of a strip of film on a screen, said film strip carryinginstruction items (4) and response items (5-8), at least one responseitem representing a correct answer, and further carrying at least oneresponse code track (a, b, c, d),

said at least one code track having a first optical density, and spotsof substantially different optical density placed in coded position onsaid at least one track at predetermined position on the film, theposition of said spots on the film being associated with previouslyselected response items, the correct answer being represented by aselected spot on a predetermined track, the spot associated with aresponse item at said predetermined track being positioned on the filmin predetermined relation with the correct response item;

a pointer (FIG. 5) adapted to be manipulated by a student to indicate aselected response item, said pointer having a photosensitive endresponsive to light values associated with the response item;

movable masking means (12) movable (50) to scan across at least theresponse code track and the response items, the mask associating lightvalues of the spot at a predetermined track with the correct responseitem;

means (32, 33) starting the scanning of said masking means at least oneoptical-electrical transducer means (21-24) located in light-receivingrelation with respect to said at 5 least one response code track;

and logic means (FIG. 6) coupled to said transducer means and to saidphotosensitive end (29) of the pointer and detecting coincidence betweenchange in light values of the photosensitive end of the pointer and aspecific transducer means associated with a specific track upon movementof said mask.

2. Machine according to claim 1 including means indexing the film stripby one or more frames;

a plurality of coded tracks and an associated transducer 1 means beingprovided;

wherein the logic circuit controls the indexing of the film strip by apredetermined number of frames in dependence on detection of coincidenceof change of light value at the photosensitive end of the pointer and atthe transducer means associated with the tracks, each track havingassigned thereto a predetermined number of frames being indexed.

3. Machine according to claim 2 answer is represented by a spot on apredetermined code track, and a spot at the predetermined track isaligned, on the film, with respect to movement of the mask with acorresponding response item;

wherein the predetermined answer corresponds to the maximum number offrames being indexed.

4. Machine according to claim 2 including circuit means controlled bysaid photosensitive end of the pointer controlling the indexing of thefilm in accordance with the number of frames commanded by said logiccircuit.

5. Machine according to claim 1 wherein the spot representing thecorrect answer is a transparent area on an opaque track;

and the transducer means is located to have a pulse transduced thereinupon scanning of said transparent area by said masking means.

6. Machine according to claim 1 wherein the response code track isopaque and the correct answer is represented by a transparent spot onthe opaque track;

and said response items are represented by bright spots projected on thescreen, the photosensitive end being adapted to respond to the brightspots on the screen upon scanning by said masking means.

7. Machine according to claim 1 wherein the response code track istransparent and the correct answer is represented by an opaque spot onthe transparent track;

and said response items are represented by bright spots projected on thescreen, the photosensitive end being adapted to respond to the brightspots on the screen upon scanning by said masking means.

8. Machine according to claim 1 wherein said mask is an opaque elementat least slightly wider than the spots to blank the spots upon scanningof the masking means for short instances of time to provide outputpulses to said transducer means, said pulses being applied to said logicmeans.

9. Machine according to claim 1 wherein said logic means includes agroup of AND gates having one input connected to said photosensitive endand another input connected to respective transducer means associatedwith a respective response code track.

10. Machine according to claim 1 including means indexing the film stripby one or more frames, and wherein the logic means includes a presetcounter (42) the output of said counter controlling the number of framesbeing indexed in accordance with sensed coincidence between the outputsfrom said photosensitive end and the transducer means, said indexingmeans stopping the film after a selected number of frames, as determinedby the counter, have been indexed.

11. Machine according to claim 1 including means indexing the film stripby one or more frames, wherein the film carries main instruction itemsand sub-instruction items and the indexing means indexes said film undercontrol of said logic circuit to present a selected sub-instructionitem, or the next main instruction item, in accordance with the answergiven by the student as indicated by presenting the photosensitive endto a selected response item.

12. Machine according to claim 1 including means indexing the film stripby one or two frames, said film carrying, in alternate sequence,sub-instruction items and main instruction items, the film having asingle response code track, the correct answer being indicated by a spotof differential optical transmissivity in a predetermined position onsaid code track.

13. Teaching machine comprising an image projector projecting an imagehaving instruction items, response items and at least one response codetrack thereon, said instruction items and said response items beingprojected on a screen;

said response items being represented by zones of differential lightflux with respect to the surrounding area of the film and said responsecode track having spots of differential light transmissivity;

first photosensitive means adapted to be placed in light receivingrelation with respect to said zones;

second photosensitive means adapted to be placed in light receivingrelation with respect to said spots;

movable masking means sequentially masking selected response items andspots; and

a logic circuit means connected to said first photosensitive means andto said second photosensitive means and detecting coincident pulses fromsaid first and said second photosensitive means and controllingsubsequent projection of images.

14. Machine according to claim 13 wherein said first photosensitivemeans is a photosensitive end of a pointer adapted to be placed by astudent at a selected zone; film transport means are provided;

and the number of frames transported by said film transport means isdetermined by said logic circuit by decoding of detected coincidence ofpulses from said photosensitive end and the pulse from said secondphotosensitive means responsive to light from a particular spot.

1. Teaching machine comprising an image projector projecting sequentialimages of a strip of film on a screen, said film strip carryinginstruction items (4) and response items (5-8), at least one responseitem representing a correct answer, and further carrying at least oneresponse code track (a, b, c, d), said at least one code track having afirst optical density, and spots of substantially different opticaldensity placed in coded position on said at least one track atpredetermined position on the film, the position of said spots on thefilm being associated with previously selected response items, thecorrect answer being represented by a selected spot on a predeterminedtrack, the spot associated with a response item at said predeterminedtrack being positioned on the film in predetermined relation with thecorrect response item; a pointer (FIG. 5) adapted to be manipulated by astudent to indicate a selected response item, said pointer having aphotosensitive end responsive to light values associated with theresponse item; movable masking means (12) movable (50) to scan across atleast the response code track and the response items, the maskassociating light values of the spot at a predetermined track with thecorrect response item; means (32, 33) starting the scanning of saidmasking means (12); at least one optical-electrical transducer means(21-24) located in light-receiving relation with respect to said atleast one response code track; and logic means (FIG. 6) coupled to saidtransducer means and to said photosensitive end (29) of the pointer anddetecting coincidence bEtween change in light values of thephotosensitive end of the pointer and a specific transducer meansassociated with a specific track upon movement of said mask.
 2. Machineaccording to claim 1 including means indexing the film strip by one ormore frames; a plurality of coded tracks and an associated transducermeans being provided; wherein the logic circuit controls the indexing ofthe film strip by a predetermined number of frames in dependence ondetection of coincidence of change of light value at the photosensitiveend of the pointer and at the transducer means associated with thetracks, each track having assigned thereto a predetermined number offrames being indexed.
 3. Machine according to claim 2 answer isrepresented by a spot on a predetermined code track, and a spot at thepredetermined track is aligned, on the film, with respect to movement ofthe mask with a corresponding response item; wherein the predeterminedanswer corresponds to the maximum number of frames being indexed. 4.Machine according to claim 2 including circuit means controlled by saidphotosensitive end of the pointer controlling the indexing of the filmin accordance with the number of frames commanded by said logic circuit.5. Machine according to claim 1 wherein the spot representing thecorrect answer is a transparent area on an opaque track; and thetransducer means is located to have a pulse transduced therein uponscanning of said transparent area by said masking means.
 6. Machineaccording to claim 1 wherein the response code track is opaque and thecorrect answer is represented by a transparent spot on the opaque track;and said response items are represented by bright spots projected on thescreen, the photosensitive end being adapted to respond to the brightspots on the screen upon scanning by said masking means.
 7. Machineaccording to claim 1 wherein the response code track is transparent andthe correct answer is represented by an opaque spot on the transparenttrack; and said response items are represented by bright spots projectedon the screen, the photosensitive end being adapted to respond to thebright spots on the screen upon scanning by said masking means. 8.Machine according to claim 1 wherein said mask is an opaque element atleast slightly wider than the spots to blank the spots upon scanning ofthe masking means for short instances of time to provide output pulsesto said transducer means, said pulses being applied to said logic means.9. Machine according to claim 1 wherein said logic means includes agroup of AND gates having one input connected to said photosensitive endand another input connected to respective transducer means associatedwith a respective response code track.
 10. Machine according to claim 1including means indexing the film strip by one or more frames, andwherein the logic means includes a preset counter (42) the output ofsaid counter controlling the number of frames being indexed inaccordance with sensed coincidence between the outputs from saidphotosensitive end and the transducer means, said indexing meansstopping the film after a selected number of frames, as determined bythe counter, have been indexed.
 11. Machine according to claim 1including means indexing the film strip by one or more frames, whereinthe film carries main instruction items and sub-instruction items andthe indexing means indexes said film under control of said logic circuitto present a selected sub-instruction item, or the next main instructionitem, in accordance with the answer given by the student as indicated bypresenting the photosensitive end to a selected response item. 12.Machine according to claim 1 including means indexing the film strip byone or two frames, said film carrying, in alternate sequence,sub-instruction items and main instruction items, the film having asingle response code track, the correct answer being indicated by a spotof differential optical transmIssivity in a predetermined position onsaid code track.
 13. Teaching machine comprising an image projectorprojecting an image having instruction items, response items and atleast one response code track thereon, said instruction items and saidresponse items being projected on a screen; said response items beingrepresented by zones of differential light flux with respect to thesurrounding area of the film and said response code track having spotsof differential light transmissivity; first photosensitive means adaptedto be placed in light receiving relation with respect to said zones;second photosensitive means adapted to be placed in light receivingrelation with respect to said spots; movable masking means sequentiallymasking selected response items and spots; and a logic circuit meansconnected to said first photosensitive means and to said secondphotosensitive means and detecting coincident pulses from said first andsaid second photosensitive means and controlling subsequent projectionof images.
 14. Machine according to claim 13 wherein said firstphotosensitive means is a photosensitive end of a pointer adapted to beplaced by a student at a selected zone; film transport means areprovided; and the number of frames transported by said film transportmeans is determined by said logic circuit by decoding of detectedcoincidence of pulses from said photosensitive end and the pulse fromsaid second photosensitive means responsive to light from a particularspot.